Start by ensuring your sushi-grade tuna is properly cubed into 1/2-inch pieces and set aside on a clean cutting board. Thinly slice the green onion (keeping white and green parts separate for now), finely mince the red onion, and grate the fresh ginger. Have your steamed rice ready at room temperature or slightly warm, and cube the avocado just before assembly to prevent browning. Measure out the edamame, seaweed salad, and sesame seeds. I prefer to do all my prep work before mixing the marinade so the tuna spends minimal time in the liquid—this keeps it tender and prevents it from becoming mushy.

In a medium bowl, whisk together the soy sauce, rice vinegar, and sesame oil until well combined. Add the minced red onion, grated ginger, and sriracha (if using heat). Gently fold in the cubed tuna, being careful not to break up the pieces, and toss until everything is evenly coated with the marinade. Let the tuna marinate for 5-10 minutes at room temperature—this timing is crucial for flavor absorption without compromising the delicate texture. I like to use a gentle folding motion rather than vigorous tossing to keep those beautiful tuna cubes intact.

Divide the steamed rice evenly between serving bowls, creating a gentle mound in the center of each. Top each rice base with the marinated tuna from Step 2, spooning any extra marinade over the top for extra flavor. Arrange the cubed avocado, edamame, and seaweed salad around the tuna in an aesthetically pleasing pattern. Finish each bowl by sprinkling sesame seeds over the top and garnishing with the sliced green onion (use the green parts for color and freshness). Serve immediately while the rice is still warm and the tuna is at its best.